What's the difference between a mp3 and wav file?

What is the difference between an MP3 and a WAV file?Is there any software to convert MP3 to WAV and viceversa?And which file tales larger size when stored on computer harddisk?

The main difference is that .Mp3 is compressed file so the file size size is reduced (around 4Mb for 4 minutes of 16bit 44KHz stereo audio). While .WAV is uncompressed and the file size is larger in size (around 40Mb for 4 minutes of 16 bit 44 KHz stereo audio).
The disadvantage of .MP3 format is that because the audio is compressed the quality is slightly reduced to the trained ear (high frequencies 3Khz and up). Also, your CD player will not recognise this format and you will need to convert it to .wav format.

wow I wrote a lot. didn't think I could! haha
hope this helps. lol

rdtallboy25's given a good explanation on the differences between the two. But basically, MP3 is compressed, WAV isn't, so a WAV file is larger.

As for software to convert between the formats, a really good one I use on occasion is Goldwave. Audacity is another one I've used with good results, although it doesn't allow all the options Goldwave does and I'm not sure if it allows you to save as an MP3.